Airbag cover

ABSTRACT

An airbag cover for an airbag unit in a motor vehicle is adapted to be torn open along predetermined lines on sudden inflation of the airbag to swing open in one or more parts along hinge lines. The cover is composed of two or more layers. A full-length tear line intended as a predetermined breaking line is provided only in the first layer on the side of the airbag.

1. The present invention relates to an airbag cover which closes an exitopening of an airbag unit in a motor vehicle.

2. Usually, such covers are visually and haptically adapted to theirinstallation surrounding. Insofar as a driver airbag is concerned, thecover has to be matched to the surface structure and colour of thesteering wheel sheating. Front passenger airbags are arranged below theinstrument panel so that the surface of the cover has to correspond withthe surface of the instrument panel as far as possible. The situation issimilar for side airbags and all other airbags to be installed in motorvehicles.

3. It can easily be understood that adapting the cover to itsinstallation surrounding often poses great problems, because the latterpossibly consists of materials which are not or only partly suitable formanufacturing a cover. Typical covers are therefore configured normallywith two or more layers, the internal layer being provided with therequired structural strength, whereas the outer layer is taylored so asto adapt to the installation surrounding. In most cases, the cover is apart of a separate airbag module which is designed for the installationon a steering wheel, an instrument panel or other internal parts of acar body. In these cases, the cover is often designated as “cover cap”,the circumferential edge of which is adapted to the size of theinstallation opening and the tear area of which, in contrast, issmaller.

4. An airbag cover may constitute an integral component of an instrumentpanel or of another internal part for motor vehicle bodies, where theadaptation to the installation surrounding generally poses no problems,but wherein the exact positioning of the tear line and the dimensioningof the predetermined breaking lines with respect to their strength canbecome difficult.

5. Hitherto it is assumed that, in the case of airbag covers configuredin two or more layers, the tear lines intended as predetermined breakinglines have to be arranged in all layers such that they have the samelength and coincide with each other, so that a defined resistance totearing can be reproducibly realized within narrow limits, because inthis respect one cannot accept an incalculable hindrance on the suddendeployment of the airbag. This, however, can be achieved in the case ofcovers configured in two or more layers only with significant productionexpenses, because for producing the individual layers separate operatingsteps are required and, mostly, also separate form tools.

6. The present invention provides an airbag cover which can be producedat a far more favorable price, without posing the need of acceptingincalculable resistances on the sudden inflation of the airbag alongpredetermined lines.

7. According to the invention, an airbag cover is provided whichconsists of two or more layers, a full-length tear line intended as apredetermined breaking line being provided only in a first one layer ofthese layers.

8. Tests have surprisingly brought the result that there is no need fora full-length tear line in the second layer and that the second layer infact tears open independently of the tear line predefined in the firstlayer when the airbag is inflated. The dynamic forces during the tearingprocess obviously are of more importance than the static tensilestrength so that any resistances to tearing hardly play a role when thefirst layer is torn open under the influence of the gas pressure waveacting in the airbag. Therefore, it is sufficient to configure a tearline intended as a predetermined breaking line in the second layer,which tear line is shorter than that of the first layer. Furthermore, ithas been found that it is sufficient to configure the tear line of thesecond layer so as to be at least partially coincident with the tearline of the first layer.

9. Further details of the invention are explained more clearly withreference to the embodiments illustrated in the FIGS. 1 and 2, in which:

10.FIG. 1 shows a first embodiment of the invention in a plan view.

11.FIG. 2 shows a second embodiment of the invention and likewise in aplan view.

12. In FIG. 1 there is illustrated a cut-out 5 of an installationsurrounding of an airbag cover 1, which for example could be part of aninstrument panel. The airbag cover 1 is configured in two layers, afull-length tear line 2 being configured in the first layer andcompleted by bending lines 4. On inflation of the airbag (not shown),the cover 1 tears open at first along the horizontally extending part ofthe tear line 2 and then along the vertically extending lines adjoiningthereto at the right and the left so that the upper and the lower partof the cover 1 can swing open about the bending or hinge lines 4. Thetear line 3 of the second layer is configured only along the horizontalextent of the tear line 2 in the first layer and is extended so as toprotrude at its ends beyond the vertical line portions by a specificlength. It has been found that a tear line 3 configured in such a way isabsolutely sufficient for ensuring a perfect tearing process. It caneasily be understood that it is much simpler during production toconfigure the tear line 3 in the second layer so as to be coincidentwith the horizontally extending part only of tear line 2 in the firstlayer, as if during production additionally also the verticallyextending sections had to be adapted to each other with respect to theirdimensions.

13. In FIG. 2 an airbag cap referenced by 6 is a component of an airbagmodule which is installed in an installation surrounding, for example,in the steering wheel or instrument panel of a motor vehicle. The cover1 is a part of the airbag cap 6 and has in the first layer a tear line 2intended as a predetermined breaking line which is arranged like in theembodiment according to FIG. 1. The predetermined breaking line 3 in thesecond layer is configured so as to correspond only with the horizontalextent of the tear line 2 of the first layer, and is also configuredonly along part of its length. Here, too, the upper and lower parts ofthe cover 1 swing open about bending or hinge lines 4. Even such a tearline 3 in the second layer can be sufficient, because the dynamic forceson the sudden inflation of the airbag are, as has been proved,sufficient to cause the further tearing of the second layer along anylines as predefined by the tear lines in the first layer.

14. It should be noted that the extension of the tear lines 2 and 3 aswell as of the bending lines 4 is only schematically depicted in theFIGS. 1 and 2 and that these lines are not visible or perceptible, atleast at the surface facing the passenger compartment.

What is claimed is:
 1. A cover for an exit opening of an airbag unit ina motor vehicle, the cover being adapted to be torn open alongpredetermined lines on sudden inflation of the airbag to swing openalong hinge lines, the cover comprising at least two layers, and only afirst one of said layers having a full-length tear line intended as apredetermined breaking line.
 2. The cover according to claim 1 , whereina partial tear line intended as a predetermined breaking line isprovided in a second one of said layers.
 3. The cover according to claim2 , wherein the tear line of the second layer is at least partiallycoincident with the tear line in the first layer.
 4. The cover accordingto claim 3 , wherein the tear line of the second layer is at leastpartially coincident with a portion of the tear line in the first layerwhich tears open first.
 5. The cover according to claim 4 , wherein thefirst layer consists of a harder material than the second layer.
 6. Thecover according to claim 5 , wherein the first layer is locatedinternally adjoining the airbag.
 7. The cover according to claim 6 ,wherein the second layer consists essentially of the same material as anupper layer of an installation surrounding of the cover.
 8. The coveraccording to claim 1 , wherein a third layer and each of any furtherlayers have no predetermined breaking line.
 9. The cover according toclaim 1 , wherein a third layer and each of any further layers have apredetermined breaking line which is not longer than the predeterminedbreaking line in the second layer.
 10. The cover according to claim 1 ,wherein the layers are interconnected by one of the group of methodsconsisting of bonding, mechanical assembling, pressing and injectionmolding.